An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non planar surface. In addition, planarization of the substrate surface is usually required for photolithography.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.
A problem in CMP is achieving a uniform thickness of the substrate layer. Variations in the slurry distribution, the polishing pad condition, the relative speed between the polishing pad and the substrate, and the dynamics of the interaction of the polishing pad and the substrate, can cause variations in the material removal rate across the substrate. These variations, as well as variations in the initial thickness of the substrate layer, cause variations in resulting thickness of the substrate layer.
Some carrier heads include multiple independently pressurizable chambers. The chambers can provide independently controllable pressures on different portions of the substrate. By providing different pressures to the different chambers, the pressure on corresponding portions of the substrate, and thus the polishing rate on those corresponding portions, can be selected to partially compensate for non-uniformity in the substrate layer.